Excellent! I'll remove the override_dh_strip targets. Is this a
product of using dh_auto_install instead of make?

No, it isn't. The Makefile contains all that, dh_auto_install just
runs 'make install'.

sorry to interrupt, but as i see it, the build process now
unconditionally strips the binaries, which violates the debian-policy
(4.9.1 DEB_BUILD_OPTIONS "nostrip")
at least, if i compile with DEB_BUILD_OPTIONS="nostrip", the resulting
binary "arraysize.pd_linux" will still be stripped.

That seems like something that debhelper should handle. Does it need
a separate install-strip Makefile target?